Self-retaining sutures including tissue retainers having improved strength

ABSTRACT

An embodiment of a suture for use in a surgical procedure applied to tissue comprises an elongated body having a first end and a second end, and a plurality of retainers arranged along a portion of the elongated body. The retainers substantially yield to motion of the elongated body within the tissue when the elongated body is drawn at the first end and resist motion of the elongated within the tissue when the elongated body is drawn at the second end. The retainers include an upper surface and a lower surface, the upper surface extending from a periphery of the elongated body and the lower surface having at least two facets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/680,176, filed Mar. 25, 2010, which is a national phase ofInternational Application No. PCT/US2008/077813, filed Sep. 26, 2008,which claims benefit of priority of U.S. Provisional Application No.60/975,758, filed Sep. 27, 2007. The complete disclosures of theaforementioned related U.S. patent applications are hereby incorporatedherein by reference for all purposes.

TECHNICAL FIELD

The present invention relates generally to methods and devices forjoining or positioning bodily tissue in surgical and cosmeticapplications.

BACKGROUND

Sutures are commonly used for closing or binding together wounds inhuman or animal tissue, such as skin, muscles, tendons, internal organs,nerves, and blood vessels. Sutures can be formed from non-absorbablematerial such as silk, nylon, polypropylene, or cotton, or alternativelysutures can be formed from bio-absorbable material such as, but notlimited to, homopolymers and/or copolymers of glycolide, lactide,p-dioxanone and ε-caprolactone.

A suture can include retainers protruding from the suture periphery andarranged to allow passage of the self-retaining suture when drawn in onedirection (with respect to the direction of protrusion of the retainer)through tissue but resist movement of the self-retaining suture whendrawn in the opposite direction. Retainers can reduce slippage of thesuture at least in a direction along the suture and can optionallyobviate knotting of the suture.

Single-directional self-retaining sutures can include an end that ispointed to allow penetration and passage through tissue when drawn bythe end and an opposite end that includes an anchor for engaging tissueat the initial insertion point to limit movement of the suture.Alternatively, bi-directional self-retaining sutures can includeretainers grouped and extending in one direction along one portion ofthe suture and opposing retainers grouped and extending in an opposingdirection along another portion of the suture. When implanted so thatboth groups of retainers are engaging tissue, the retainers can resistmovement of the suture through tissue in either direction.

A surgeon may use a surgical needle with an attached suture (which canbe a smooth monofilament or can be a multi-filament) to pierce thetissue alternately on opposing faces of a wound to sew the wound closed.Techniques for placement of self-retaining sutures in tissue to close orbind together wounds can include threading the self-retaining suture instraight-line patterns such as zig-zag, and curvilinear patterns such asalpha, sinusoidal, and corkscrew. A surgeon may also use self-retainingsutures to position and support tissue where there is no wound inprocedures such as cosmetic surgery of the face, neck, abdominal orthoracic region among others.

BRIEF SUMMARY OF THE INVENTION

Briefly stated, the present invention provides sutures, methods offorming retainers in a suture, systems useful to form a retainer in asuture, and related technology.

Within one aspect of the present invention, a suture is provided, thesuture being useful in a procedure applied to tissue, where the suturecomprises: an elongated body having a first end and a second end; and aplurality of retainers arranged along a portion of the elongated body;wherein the retainers substantially yield to motion of the elongatedbody within the tissue when the elongated body is drawn in a firstdirection and resist motion of the elongated within the tissue when theelongated body is drawn in a second direction opposite the firstdirection; and wherein the retainers include an upper surface and alower surface, the upper surface extending from a periphery of theelongated body and the lower surface having at least two facets. Withinvarious optional embodiments, which may be combined or not, (a) one orboth of the elongated body and the plurality of retainers includes anassociated material to be delivered to the tissue, where optionally, theassociated material is one or more of a hormone, a drug, and medicine;(b) the plurality of retainers is a first set and the portion of theelongated body is a first portion; and further comprising: a second setincluding a plurality of retainers arranged along a second portion ofthe elongated body; wherein the retainers substantially yield to motionof the elongated body within the tissue when the elongated body is drawnat the second end and resist motion of the elongated within the tissuewhen the elongated body is drawn at the first end; and wherein theretainers of the second set include an upper surface and a lowersurface, the upper surface extending from a periphery of the elongatedbody and the lower surface having at least two facets.

Within another aspect, the present invention provides a method offorming one or more retainers in a suture having an elongated body witha first end and a second end for use in a surgical procedure applied totissue, where the method comprises: positioning the elongated body;oscillating a cutting edge so that the cutting edge alternatelypenetrates the elongated body and exits the elongated body, wherein thecutting edge includes a first blade and a second blade arranged to forman angle; wherein the cutting edge forms one or more retainers so thatthe one or more retainers substantially yield to motion of the elongatedbody within the tissue when the elongated body is drawn at the first endand resist motion of the elongated within the tissue when the elongatedbody is drawn at the second end. Within various optional embodiments,which may be combined for not, (a) the method further comprises heatingthe cutting edge so that the one or more retainers are annealed, whereoptionally the cutting edge is heated to approximately 200° C.; (b) thefirst blade and the second blade as used in the method comprisesapphire.

Within another aspect, the present invention provides a suture for usein a procedure applied to tissue, where the suture comprises: anelongated body having a first end and a second end; and a plurality ofretainers arranged along a portion of the elongated body; wherein theretainers substantially yield to motion of the elongated body within thetissue when the elongated body is drawn at the first end and resistmotion of the elongated within the tissue when the elongated body isdrawn at the second end; and wherein the retainers include an uppersurface and a lower surface formed by a cutting edge, the upper surfaceextending from a periphery of the elongated body and the lower surfacejoining the elongated body at an apex having a radius of curvaturelarger than a radius of curvature of the cutting edge. Within variousoptional embodiments, which may be combined or not, (a) one or both ofthe elongated body and the plurality of retainers includes an associatedmaterial to be delivered to the tissue, where optionally the associatedmaterial is one or more of a hormone, a drug, and medicine; (b) theradius of curvature of the apex is up to 0.5 times the retainer channelopening length; (c) the radius of curvature of the apex is 0.1 to 0.25times the retainer channel opening length; (d) the plurality ofretainers is a first set, the portion of the elongated body is a firstportion, and the cutting edge is a first cutting edge; and furthercomprising: a second set including a plurality of retainers arrangedalong a second portion of the elongated body; wherein the retainerssubstantially yield to motion of the elongated body within the tissuewhen the elongated body is drawn at the second end and resist motion ofthe elongated within the tissue when the elongated body is drawn at thefirst end; and wherein the retainers of the second set include an uppersurface and a lower surface defined by a second cutting edge, the uppersurface extending from a periphery of the elongated body and the lowersurface joining the elongated body at an apex having a radius ofcurvature larger than a radius of curvature of the second cutting edge.

Within another aspect, the present invention provides a method offorming one or more retainers in a suture for use in a surgicalprocedure applied to tissue comprising: positioning an elongated bodyhaving a first end and a second end; heating a cutting edge to atemperature that distorts the elongated body; and oscillating thecutting edge so that the cutting edge alternately penetrates theelongated body and exits the elongated body; wherein the cutting edgeforms the one or more retainers so that the one or more retainerssubstantially yield to motion of the elongated body within the tissuewhen the elongated body is drawn at the first end and resist motion ofthe elongated within the tissue when the elongated body is drawn at thesecond end; and wherein the cutting edge forms the one or more retainersto include an upper surface and a lower surface defined by a cuttingedge, the upper surface extending from a periphery of the elongated bodyand the lower surface joining the elongated body at an apex having aradius of curvature larger than a radius of curvature of the cuttingedge. In various optional embodiments, which may be combined, (a) themethod further comprises annealing the one or more retainers with thecutting edge, optionally wherein the one or more retainers are annealedby heating the cutting edge within the range of 100-250° C.; (b) theradius of curvature of the apex is up to 0.5 times the retainer channelopening length, for example, the radius of curvature of the apex is 0.1to 0.25 times the retainer channel opening length; and (c) the lowersurface is one of V-shaped, rectangular-shaped, and trapezoidal-shaped.

Within another aspect, the present invention provides a system to form aretainer in a suture for use in a procedure applied to tissue, thesystem comprising: a cutting edge including a first blade and a secondblade arranged at an angle relative to the first blade; a mechanism tooscillate the cutting edge; and a heater connected with the cutting edgeto heat the cutting edge. In various optional embodiments, which may becombined, (a) the first blade and the second blade are sapphire blades;(b) the first blade and the second blade are one of metallic blades andceramic blades; (c) the first blade and the second blade aresubstantially in contact and the second blade is arranged at 90°relative to the first blade; (d) the heater is a copper plate thatconducts heat to the cutting edge; (e) the mechanism to oscillate thecutting edge is a cam.

Within another aspect, the present invention provides a suture for usein a procedure applied to tissue, where the suture comprises: anelongated body having a first end and a second end; and a plurality ofretainers arranged along a portion of the elongated body; wherein theretainers substantially yield to motion of the elongated body within thetissue when the elongated body is drawn at the first end and resistmotion of the elongated within the tissue when the elongated body isdrawn at the second end; and wherein the retainers include an uppersurface and a lower surface formed by a cutting edge, and wherein theupper surface includes a supplementary material formed on at least aportion of the upper surface. In various optional embodiments, which maybe combined, (a) the supplementary material is deposited by a printingtechnique; (b) the supplementary material has substantially the samematerial properties as the elongated body; (c) the supplementarymaterial has one or both of higher yield strength and higher Young'sModulus than the elongated body.

Within another aspect, the present invention provides a suture for usein a procedure applied to tissue, where the suture comprises: anelongated body having a first end and a second end; and a plurality ofretainers arranged along a portion of the elongated body; wherein theretainers substantially yield to motion of the elongated body within thetissue when the elongated body is drawn at the first end and resistmotion of the elongated within the tissue when the elongated body isdrawn at the second end; and wherein a spacing distance is formedbetween retainers arranged at a position along a circumference of theelongated body, the spacing distance being a function of the tissuestrength and composition.

The details of one or more embodiments are set forth in the descriptionbelow. Other features, objects and advantages will be apparent from thedescription, the drawings, and the claims. In addition, the disclosuresof all patents and patent application referenced herein are incorporatedby reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details of the present invention are explained with the help ofthe attached drawings in which:

FIG. 1A is a side view of a suture in accordance with the prior artincluding a retainer protruding generally at an angle in a directionalong an axis of the suture.

FIG. 1B is a perspective view of the suture of FIG. 1A.

FIG. 2A is a side view of an embodiment of a suture including a retainerwherein an apex of a cut forming the retainer is enlarged to distributeapplied stress applied across a larger surface, reducing concentrationof the stress.

FIG. 2B is a perspective view of the suture of FIG. 2A.

FIG. 3 is a side view of an improperly formed retainer.

FIG. 4A is a side view of an embodiment of a suture including a retainerwherein the retainer has a lower surface having two converging faces.

FIG. 4B is a front view of the embodiment of FIG. 4A.

FIG. 4C is a front view of an alternative embodiment of a sutureincluding a retainer wherein the retainer has a lower surface havingthree facets, where adjacent facets are converging.

FIG. 5A top perspective view of a blade configuration for forming theretainer of the suture of FIGS. 4A and 4B.

FIG. 5B top perspective view of a blade configuration for forming theretainer of the suture of FIG. 4C.

FIG. 6A is a side view of an alternative embodiment of a sutureincluding a retainer with material added to a surface of the retainer.

FIG. 6B is a top view of the suture of FIG. 6A including a retainer withmaterial added to a surface of the retainer.

FIG. 7A is a side view of a suture including a plurality of retainersprotruding from approximately the same tangent along a periphery of thesuture, and spaced so that the retainers overlap a preceding retainer orare overlapped by a subsequent retainer along the suture.

FIG. 7B is a side view of a suture including a pair of retainersprotruding from approximately the same tangent along a periphery of thesuture. The pair of retainers is spaced a distance along the suture.

FIG. 7C is an exploded diagram illustrating relative size of tissue andrelated structures.

DETAILED DESCRIPTION

Self-retaining sutures used in surgical techniques such as wound closureand tissue positioning can provide improved results where the retainersof the sutures provide increased resistance to movement opposite thepath of insertion (also referred to hereinafter as “pull-out strength”).Pull-out strength can vary with factors such as retainer geometry,relative positioning of the retainers along the suture, the type oftissue into which the suture is implanted, the surgical or cosmetictechnique applied for implantation of the suture, the strength of thecore suture, and application for which the suture is used. For example,suture performance may be identified with reference to tissue type, withdifferent sutures being qualified for use in surgical procedurestargeting specific tissue. Different tissues will accept favorablydifferent configurations, spacing, and geometries of the retainers.Suturing muscle in an abdomen, for example, can be substantiallydifferent from sewing fatty tissue or skin tissue. Sutures can belabeled to identify appropriate procedures and tissue.

Self-retaining suture refers to a suture that may not require a knot inorder to maintain its position into which it is deployed during asurgical procedure. Such self-retaining sutures generally include aretaining element or tissue retainer.

Tissue retainer refers to a suture element having a retainer bodyprojecting from the suture body and a retainer end adapted to penetratetissue. Each retainer is adapted to resist movement of the suture in adirection other than the direction in which the suture is deployed intothe tissue by the surgeon, by being oriented to substantially face thedeployment direction (i.e. the retainers lie flat when pulled in thedeployment direction; and open or “fan out” when pulled in a directioncontrary to the deployment direction). As the tissue-penetrating end ofeach retainer faces away from the deployment direction when movingthrough tissue during deployment, the tissue retainers should generallyavoid catching or grabbing tissue during this phase. Once theself-retaining suture has been deployed, a force exerted in anotherdirection (often substantially opposite to the deployment direction)causes the retainers to be displaced from their deployment positions(i.e. resting substantially along the suture body), forces the retainerends to open (or “fan out”) from the suture body in a manner thatcatches and penetrates into the surrounding tissue, and results intissue being caught between the retainer and the suture body; thereby“anchoring” or affixing the self retaining suture in place. By way ofexample only, tissue retainer or retainers can include hooks,projections, barbs, darts, extensions, bulges, anchors, protuberances,spurs, bumps, points, cogs, tissue engagers, tractions means, surfaceroughness, surface irregularities, surface defects, edges, facets andthe like.

FIG. 1A is a side view and FIG. 1B is a perspective view of a suture 100in accordance with the prior art including a retainer 102 protrudingfrom a periphery of the suture 100. Retainers can have myriad geometricshapes, for example pyramidal and conical. The retainer 102 is formedwhen a cutting edge (not shown) is brought into contact with the suture100 so that the cutting edge 102 penetrates the periphery of the suture100. The cutting edge forms a wedge cut 106 having an apex 104 at atermination point of the cutting edge's penetration. The retainer 102 isurged apart from the suture 100 so that the retainer 102 is gapped toform a retainer channel opening x from the periphery of the suture 100from which the retainer 102 is separated. The apex 104 likely includes asmall radius of curvature defined largely by a rounding of the cuttingedge. For example, the cutting edge may be a knife blade includingrounding inherent in a structure subjected to abrasion forces, or forexample the cutting edge may be a wire having a circular cross-sectionwith a diameter. It can be desirable for the cutting edge to have anextremely small radius of curvature (i.e., to be a sharp as practicable)so that the periphery of the suture is penetrated cleanly. The extremelysmall rounding of the cutting edge results in a sharp apex 104, whichproduces an unfavorably high stress concentration.

In a common surgical or cosmetic procedure, the suture of FIGS. 1A and1B may be threaded or otherwise inserted into tissue and drawn in thedirection of a first end 108. The force of the tissue pressing againstthe suture 100 causes the retainer 102 to substantially collapse andyield to movement of the suture through the tissue. If the suture 100 isdrawn in the direction of a second, opposite end 110, the edge of theretainer 102 grabs the tissue and resists movement. Additional forceapplied to the suture 100 can increase the retainer channel opening x,causing a high stress concentration at the apex 104. This results in anincreased probability of fracture initiation and propagation at the apexresulting in suture failure.

Referring to FIGS. 2A and 2B, an embodiment of a self-retaining suture200 in accordance with the present invention can include a retainer 202formed by a cut 206 with an apex 204 radius of curvature larger than aradius of curvature of the cutting blade (not shown). In a preferredembodiment, the radius of curvature of the apex 204 can range from 0.1to 0.25 times the retainer channel opening x, although in otherembodiments the radius of curvature of the apex 204 can be smaller than0.1× or larger than 0.25×(e.g., 0.5×). Stress reduction at the apex ofthe cut can be achieved by increasing a radius of curvature at the apex204 of the cut 206. Embodiments of methods in accordance with thepresent invention can be applied to form sutures within the periphery ofthe suture have an apex larger than the cutting blade. Alternatively,the apex geometry can be non-circular (i.e. the groove terminating in aflat face, a multi-faced facet, or any other given geometric shape orcombination thereof).

In an embodiment of a method, a heated cutting edge such as a blade orwire can penetrate the periphery of the suture, heating the suturematerial as the knife cuts. The temperature and contact time can bevaried to achieve the most desirable curvature of the apex. Preferably,the cutting edge can be heated to a temperature between the meltingtemperature of the suture material and the decomposition temperature ofthe suture material. For example, polyethylene terephthalate can have amelting temperature of about 260° C. and a decomposition temperature ofabout 350° C., some polyglycolic acid homopolymers can have a meltingtemperature of about 180° C. and a decomposition temperature of about225° C., some types of nylon can have a melting temperature of about250° C. and a decomposition temperature of about 375° C., andpolydioxanone can have a melting temperature of about 90° C. and adecomposition temperature of about 175° C. It should be noted that thesetemperature characteristics are exemplary, and melting and decompositiontemperatures may vary within a class of materials. For example, nylonmelting and decomposition temperatures can vary substantially based onthe chemical composition.

In an alternative embodiment of a method of increasing the radius ofcurvature of the apex, a first cutting edge can form the retainer (andcut), and a second heated edge or blunt heated dye can be subsequentlypositioned within the cut. A still further embodiment of a method ofincreasing the radius of curvature of the apex can comprise a two-stepcut, whereby a first cutting edge (e.g., a knife blade or wire) havingan edge with a first radius of curvature penetrates the periphery of thesuture to cause a cut, followed by a second cutting edge having an edgewith a second, larger radius of curvature to widen the apex of the cut.The temperature, radius of curvature of the dye, pressure applied duringforming and contact time can be varied to achieve the most desirablecurvature.

A common technique for forming retainers on sutures includes feeding ordrawing the suture across a pulley (also called an anvil). As the suturetwists, a cutting edge slices across the suture, forming retainers.Twisting the suture may or may not affect the mechanical properties ofthe suture along an unaltered periphery of the suture and/or at theretainer. In an alternative embodiment, a method of forming a sutureincluding retainers having a cut with a radius of curvature larger thana cutting edge can include feeding or drawing a suture from a feed spoolto a take-up spool that are spinning at a matched angular velocity. Acutting edge is heated to a temperature sufficient to melt a materialwith which the suture is formed, and the cutting edge is rotated acrossthe surface of the suture to form the retainers. The cutting edge can beheated by any known technique for heating small precision tools, to atemperature sufficient to cause a desired melting of the suture materialwithout causing undesired stretching, mechanical deformation orexcessive diameter reduction. For example, a conductive blade or wirecan be heated by resistive heating to a temperature of approximately 200degrees C. Alternatively, where achievable, one or both of the cuttingedge and the suture can be heated by a laser, directed gas, flame ortorch so that when the cutting edge penetrates the suture to form aretainer, a local temperature near the apex of the cut is sufficient toachieve a desired geometric result. Where a laser is used to heat thesuture, a polymer or copolymer comprising the suture can be doped toabsorb the wavelengths of the laser. The area to which the heatingsource is directed can be as small as 10 nanometers across.

Referring to FIG. 3, a cut 304 caused by a cutting edge with intent toform a retainer is shown that is generally non-protruding from theperiphery of the suture 300. Such a result can occur where a materialhas insufficient plasticity and is predominantly deformed in the elasticregion during retainer cutting. A retainer formed in such a materialwill tend to lay flat rather than “stand up” by protruding from theperiphery. A retainer that fails to protrude from the periphery is lesslikely to catch the tissue in which it is arranged. Mechanicalproperties of the specific suture material are considered in order toform a retainer geometry having preferred characteristics. A retainerformed in a material having undesirably high elasticity can have animproved protrusion from the periphery of the suture by annealing thelocal suture material at least at the base of a retainer site. Annealingthe base of the retainer causes polymer chains to realign themselves andrelieves internal stresses in a polymer. During cutting, these residualstresses may cause the retainers to lay flat. Relieving the residualstresses at the base of the retainer by annealing can allow theretainers to protrude from the periphery of the suture.

To anneal a polymer, the polymer is heated to a temperature above somecrystallization temperature for an amount of time to change itsmicrostructure, and then cooled at a given rate to retain or obtain adifferent microstructure. For example, the crystallization temperaturefor polydioxanone is about 40° C., while a crystallization temperaturefor a copolymer of glycolide ε-caprolactone in a 72/28 ratio is about75° C. Sutures are typically formed from extruded polymer and areannealed after extrusion to relieve some of the alignment of polymerchains, to recover some elongation, and to drive out residual solvents.The sutures can subsequently be heated in an oven over a period of timeto sterilize the sutures. Some annealing can occur during sterilization;although where sutures are sterilized using techniques employingrelatively low temperatures (such as sterilization by ethylene oxide)the annealing is typically not effective in reducing internal stresses.The semi-crystalline structure that results from processing provides asuture with mixed properties including high yield strength andacceptable malleability.

In a preferred embodiment, annealing of the cut retainer is achieved bylocal heating of the retainer at the base of the retainer while theretainer is protruding to a generally desired degree. Local heating ofthe retainer can be achieved (as described above with reference toincreasing a radius of curvature of the apex) by heating the cuttingedge to a sufficient temperature. As mentioned above, a cutting edge canbe heated by resistive heating, or by other conductive or convectivemeans. Alternatively, the retainer can be heated by heated gas (such ashot nitrogen gas), a flame, a torch or some other heat source. It isproposed that heating with a cutting edge at a sufficient temperature(e.g., 200 degrees C.) for 4-5 milliseconds, and cooling by ambienttemperature, can result in a sufficiently protruding retainer.Alternatively, the retainer can be actively cooled. For example, aPeltier device is a device for electrically controlling temperature thatcan be miniaturized to suit small features.

Referring to FIGS. 4A and 4B, an alternative embodiment of aself-retaining suture 400 in accordance with the present invention caninclude a retainer 402 with an upper surface 412 extending from aperiphery 410 of the elongated body and a lower surface 414 having atleast two facets 416. As seen in the front view of FIG. 4B, the retainercan have a roughly pie-slice (i.e., wedge) shape. The increasedcross-section moment of inertia (also known as the second moment ofarea) of the retainer improves strength, and can improve resistance tothe tendency of a retainer to fold back on itself and yield to movementof the suture through the tissue, as described above. This retainerfurther reduces stress concentrations along the lower surface of theretainer and the suture when compared with the retainers of FIG. 1A. Theretainer need not be shaped as a perfect wedge, but rather preferablyhas at least two facets to improve resistance to back bending. Thus, forexample in FIGS. 4C and 5B, a suture 600 is shown having a retainer 602having a roughly trapezoidal shape, with three facets 616.

Referring to FIG. 5A, an embodiment of a method of forming a retainer402 in a suture 400 such as shown in FIGS. 4A and 4B is illustrated. AV-shape cutting edge 420 can be formed arranging two blades 422,424 inproximity to form a desired cutting angle α and resembling a V.Preferably, the blades 422,424 can be placed close to each other at acutting angle α of 90°, although the blades 422,424 can be arranged toform an obtuse or acute angle where desired. The cutting edge 420 canoptionally be heated to provide local heating to the base of theretainer 402 while cutting the suture 400, thereby annealing the base ofthe retainer 402 and/or increasing a radius of curvature at apex 404 orthe interface of the lower surface 414 of the retainer 402 and thesuture 400. In a preferred embodiment, the cutting edge 420 can comprisesapphire blades. Sapphire blades are ceramic blades typically having anedge radius one or two magnitudes lower than an edge radius of a steelblade. Further, sapphire blades generally maintain their mechanicalcharacteristics over the temperature ranges desirable for annealingpolymer and co-polymer materials. Maintaining mechanical characteristics(i.e., geometry of a cut produced) can be desired where the retainersare extremely small and therefore sensitive to small changes. Further,sapphire blades are more abrasion resistant than, for example, typicalsteel blades, providing more repeatable results over long term use.Further, sapphire blades can be sharpened more effectively than steelblades. In another embodiment of this invention the V-shaped blade canhave any of its surfaces be convex or concave to allow for the selectionof an appropriate final retainer design, either maximizing the moment ofinertia of the retainer or the remaining cross sectional area of thesuture.

In an embodiment, the suture 400 can be spooled or otherwise fed ordrawn in a direction z after extrusion at a generally constant speed, ina non-twisting path. For manufacturing a one-direction retainer suture,a cutting edge 420 can be arranged in each of four quadrants of acircle. The cutting edge 420 can comprise the sapphire blades thatoscillate in a direction z so that the cutting edge 420 alternatelypenetrates the suture 420 and pulls away from a cut. As mentioned, thecutting edge 420 is heated to both cut and anneal the retainer 402simultaneously, causing the retainer 402 to protrude from the peripheryof the suture 400. The cutting edge can be oscillated by a cam device,for example.

To heat the cutting edge 420, the sapphire blades can be mounted orotherwise place in conductive communication with a copper heating plate430. The copper plate 430 can heat the cutting edge 420 throughconduction to a temperature above the crystallization temperature of thesuture material. For example, where the suture material is a copolymerof glycolide ε-caprolactone the cutting edge can be heated to about 200°C. The temperature of the cutting edge can be maintained in atemperature range to provide satisfactory results. The cutting edge 420is generally in conductive proximity to the retainer 402 for generallyfrom four to five milliseconds. In this embodiment, heating the retainerat 200° C. for four to five milliseconds is sufficient to anneal thebase of the retainer so that the retainer protrudes from the peripheryof the suture. It may be desirable to cause sufficient contact to meltthe suture at the apex, thereby increasing a radius of curvature of theapex. The retainers are cooled by the ambient conditions of theenvironment (generally room temperature) or through directed cooling toprovide a desired degree of strand alignment (crystallinity) in thematerial. Alternatively, the sapphire blades can be heated by a laserbeam directed through the sapphire blades. An efficiency of thistechnique can depend on the absorption of the suture material.

Referring to FIG. 5B, a cutting edge 620 includes two sapphire blades624 having some finite distance between the cutting surfaces, resultingin a suture 600 having a retainer 602 resembling the retainer 602 ofFIG. 4B. Further, an alternative heating plate 630 is shown contactingthe surface of the blades 624 rather than contacting the back edge ofthe blades 624.

For manufacturing a two-direction retainer suture, a cutting edge can bearranged in each of four quadrants of a circle in each of two directionsof protrusion/penetration, resulting in eight cutting edges. The cuttingedge can comprise the sapphire blades that oscillate so that the cuttingedge alternately penetrates the suture and pulls away from the cut. Asmentioned, the cutting edge is optionally heated to both cut and annealthe retainer simultaneously, causing the retainer to protrude from theperiphery of the suture.

In other embodiments of methods of forming retainers in sutures inaccordance with the present invention, other retainer arrangements canbe produced. For example, a cutting edge can be arranged in each ofthree zones to form retainers extending from three circumferentiallocations along the suture. Alternatively, one or more cutting edges canbe rotated so that the retainers are arranged in a helical fashion alongthe suture. Retainer patterns can be formed to suit a surgical orcosmetic procedure or application, and the properties of the material atthe location of the procedure or application.

Referring to FIGS. 6A and 6B, a still further embodiment of aself-retaining suture 500 in accordance with the present invention caninclude a retainer 502 having supplementary material 540 on an uppersurface 512 of the retainer 502. The supplementary material 540 canincrease the mass of the retainer 502 to improve strength and improveresistance to the tendency of the retainer 502 to fold back on itselfand yield to movement of the suture 500 through the tissue, as describedabove. The supplementary material 540 can comprise a polymer orcopolymer that is the same material used to form the suture 502, or apolymer or copolymer material different from the material used to formthe suture 500. Alternatively, the supplementary material 540 can besome other material (preferably biocompatible with the tissue in whichit is implanted) that can be made to adhere to the upper surface 512 ofthe retainer 500. Such materials can include metals, ceramics, polymers,composites, or a combination thereof. Preferably, the supplementarymaterial can comprise a material that is stiffer and stronger than thematerial with which the suture is formed (i.e., the material can have anincreased Young's modulus and/or an increased yield strength andultimate tensile strength). The supplementary material 540 can be formedor deposited before the cutting edge forms the retainer 502 oralternatively the supplementary material 540 can be formed subsequent toforming the protruding retainer 502; however, the supplementary material540 is generally confined to the surface of the retainer 502. Preferablythe supplementary material 540 increases a mean thickness of theretainer up to twice the thickness of the retainer without thesupplementary material.

In an embodiment, a printer can used to precisely deposit thesupplementary material 540 on the location where the retainer 502 is orwill be formed. The printer can be, for example, a dot matrix styleprinter having a wire or pin that runs back and forth along the sutureand prints by impact, striking the location where the retainer is orwill be formed to cause the supplementary material to be deposited.Alternatively, some other printing technique can be applied, such astechniques resembling inkjet printing techniques. In still otherembodiments, the supplementary material can be deposited or formed usingsome technique other than printing, such as brush coating, spraycoating, selective dip coating, curtain coating, etc.

It is noted that embodiments of sutures in accordance with the presentinvention can further be impregnated, coated, or otherwise associatedwith medicine, hormones, drugs, etc., to deliver the associated materialto the surgical location. Such associated treatments can be released asthe suture material is absorbed into the body. For example,polydioxanone (specifically poly(p-dioxanone)) is a biopolymer thatloses most of its strength within six to eight weeks and begins toabsorb in about three to four months, and is therefore a longer-termdegradable. Polyglycolide and ε-caprolactone, which are degradedprimarily by hydrolysis, dissolve generally in a shorter timeframe thanpolydioxanone. In such embodiments, the associated material can assistin healing wounds closed with the sutures, or alternatively, the sutureitself can serve primarily as a vehicle for delivering the associatedmaterial over a period of bio-absorption.

FIG. 7A is a side view of a suture 600 including a plurality ofretainers 602 protruding from approximately the same tangent along aperiphery of the suture 600, and spaced so that the retainers overlap apreceding retainer 602 or overlapped by a subsequent retainer 602 alongthe suture 600. FIG. 7B is a side view of a suture 700 including a pairof retainers 702 protruding from approximately the same position alongthe circumference of the suture, the pair of retainers 702 spaced adistance, L, along the suture 700. As the retainers 700 are arrangedcloser together (i.e., L is reduced) so that the retainers approach apoint of overlapping (as shown in FIG. 7A), the target location of thesurgical or cosmetic procedure can begin to “see” the retainers as acontinuous surface, so that the retainers fail to grab or interfere withsuture movement through the target location in a direction opposite thedirection of insertion. The degree of overlap or proximity that resultsin undesirable retainer performance can vary depending on tissue type.Referring to FIG. 7C, for example, when retainers grab or interfere withsuture movement through muscle, the retainer commonly grabs orinterferes with bundles of muscle, rather than microfibers. On the otherhand, when retainers grab or interfere with suture movement throughcollagen, the retainers typically grab or interfere with collagen fibers(collagen fibrils are tropocollagens packed into an organizedoverlapping bundle, while collagen fibers are bundles of fibrils).Collagen fibers can have diameters approaching 10 μm. An acceptableproximity or overlap of retainers can generally be proportional to thesize of the structure in which the retainers are placed, so that closelyarranged retainers are generally acceptable for tissue and structurecomprised of microfibers or other small structures, for example.Generally, longer spacing between retainers (i.e., where distance L islarge) is appropriate for tissues with relatively larger structures thatcan support the retainer. In addition, the distance between retainers Lcan be a function of the strength of the tissue. Overall, a strongertissue can accommodate a larger retainer distance L and a weaker tissuecan accommodate a shorter retainer distance L. Another way to view thedependence of the distance L on the tissue is that a length of tissueequal to L resists the hold of a single retainer. Failure can occureither if the retainer or the tissue opposing the retainer fails. If thedistance between retainers L is increasingly small the force which thetissue can withstand also becomes small, whereas if the distance betweenretainers L is increasingly large the force that the tissue canwithstand is excessively large. An equilibrium case L would be such thatthe force that the tissue (length L) can withstand is equal to the forceit takes to bend back or break off the retainer. This distance L is afunction of the type of tissue where the suture is used. As such, thistranslates into the amount of retainers per length of suture beingoptimized for each particular type of tissue.

The foregoing description of the present invention has been presentedfor purposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise forms disclosed.Many modifications and variations will be apparent to practitionersskilled in this art. The embodiments were chosen and described in orderto best explain the principles of the invention and its practicalapplication, thereby enabling others skilled in the art to understandthe invention for various embodiments and with various modifications asare suited to the particular use contemplated. It is intended that thescope of the invention be defined by the following claims and theirequivalents.

The invention claimed is:
 1. A method of forming one or more retainersin a suture having an elongated body with a first end and a second endfor use in a surgical procedure applied to tissue comprising:positioning the elongated body; oscillating a heated cutting edge sothat the heated cutting edge alternately penetrates the elongated bodyand exits the elongated body, wherein the heated cutting edge includes afirst blade and a second blade arranged to form an angle; wherein theheated cutting edge forms the one or more retainers so that the one ormore retainers substantially yield to motion of the elongated bodywithin the tissue when the elongated body is drawn at the first end andresist motion of the elongated body within the tissue when the elongatedbody is drawn at the second end, and wherein said one or more retainersare annealed with the heated cutting edge.
 2. The method of claim 1,wherein the cutting edge is heated to approximately 200° C.
 3. Themethod of claim 1, wherein the first blade and the second blade comprisesapphire.